POLAR RESEARCH, 2017 VOL. 36, 1297915 https://doi.org/10.1080/17518369.2017.1297915 RESEARCH ARTICLE Molluscan assemblages associated with Gigartina beds in the Strait of Magellan and the South Shetland Islands (Antarctica): a comparison of composition and abundance Sebastián Rosenfelda,b, Cristian Aldeac,d, Jaime Ojeda a, Johanna Marambioa,b, Mathias Hünee, Jesús S. Troncosof & Andrés Mansillaa,b aLaboratorio de Macroalgas Antárticas y Subantárticas, Universidad de Magallanes, Punta Arenas, Chile; bInstituto de Ecología y Biodiversidad (IEB), Santiago, Chile; cDepartamento de Ciencias y Recursos Naturales, Universidad de Magallanes, Punta Arenas, Chile; dPrograma GAIA-Antártica, Universidad de Magallanes, Punta Arenas, Chile; eFundación Ictiológica, Santiago, Chile; fDepartamento de Ecología y Biología Animal, Facultad de Ciencias del Mar, Universidad de Vigo, Vigo, Spain ABSTRACT KEYWORDS In this paper we evaluated the composition and abundance of molluscs associated with beds Bivalvia; Gastropoda; of the red algae Gigartina, located in the South Shetland Islands (Antarctic Peninsula) and the Polyplacophora; algae beds; Strait of Magellan (southern Chile). During the summer season of 2013, samples were sub-Antarctic; diversity 2 obtained by scuba diving using a 0.25 m quadrat, arranged randomly within the bed. We ABBREVIATIONS extracted a total of 15 quadrats per sampling site. For Antarctic Peninsula beds the most MBP: Magellanic abundant species were the bivalve Lissarca miliaris (233 individuals) and the gastropod biogeographical province; Laevilacunaria antarctica (94 individuals), while for Strait of Magellan beds the most abundant NMDS: non-metric species was the polyplacophoran Callochiton puniceus (36 individuals). Comparative analysis multidimensional scaling between the two molluscan assemblages showed significant differences in the faunal com- ordination position between the Antarctic Peninsula and Strait of Magellan (f = 64.474; p = 0.0001). Therefore, molluscs reported in both areas are characteristic of their respective biogeographic area. Finally, Gigartina species play an important role in the formation of patterns of abun- dance and diversity of the communities associated with them. – Introduction beds reaching biomasses of about 1773 g m 2 and – densities of 15 individuals m 2 (Ávila et al. 2004). In the high-latitude MBP (Spalding et al. 2007), exten- Besides being primary producers and ecosystem engi- sive macroalgae assemblages grow on hard substrates, neers (Christie et al. 2009;Torresetal.2015), macro- between depths of approximately 0 and 20 m (Mansilla algae beds are important for sustenance of biodiversity et al. 2013). These communities of macroalgae are char- because they can alter local environmental conditions acterized mainly by the presence of species of the order (Stachowicz 2001), providing shelter, breeding places Laminariales, such as Macrocystis pyrifera and Lessonia and/or food for many species of invertebrates and ver- spp. (Mansilla et al. 2014; Rosenfeld et al. 2014). In the tebrates (Ríos et al. 2007; Mansilla & Ávila 2011; Antarctic Peninsula, macroalgae communities are char- Rosenfeld et al. 2015). Molluscs are one of the most acterized by the presence of species of Desmarestia representative and studied groups worldwide of this (Quartino et al. 2005). However, the Rhodophyta algae algae–mollusc interaction (see Vahl 1971;Salas& Gigartina skottsbergii is a characteristic species of the Hergueta 1986; Sánchez-Moyano et al. 2000;Rueda& southern tip of South America (Ramírez & Santelices Salas 2003;Amsleretal.2015;Martinetal.2016). 1991) and West Antarctica; it is therefore a species from In the MBP, molluscs are one of the most represen- cold-temperate to cold waters. In the sub-Antarctic tative and diverse groups of benthic marine environ- ecoregion this species is strictly sublittoral and grows ments, with more than 397 species reported (Linse on rocky substrate between 5 and 15 m deep (Ávila et al. 1999; Valdovinos 1999). Another important feature of 1999). Nevertheless Billard et al. (2015) show that G. Magellanic molluscs is that 35% of species are endemic skottsbergii has two divergent, monophyletic clades that to the MBP (Fortes & Absalao 2011). Among the mol- may correspond to two cryptic species, making luscs, gastropods are the dominant group in terms of Gigartina sp. from Antarctica endemic to this area. In number of species, followed by bivalves (Linse et al. Antarctica it may live from the lower intertidal zone 2006; Clarke et al. 2007). Clarke et al. (2007)recorded (pers. obs.) to shallow depths (Wiencke & Clayton a total of 549 species of gastropods and 158 bivalves 2002). Gigartina skottsbergii forms dense sublittoral CONTACT Sebastián Rosenfeld [email protected] Sekulovic, Laboratorio de Macroalgas Antárticas y Subantárticas, Universidad de Magallanes, Casilla 113-D, Punta Arenas Chile Supplemental data for this article can be accessed here. © 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 S. ROSENFELD ET AL. distributed in the Southern Ocean. Engl (2012) reported Ana, located 60 km to the south of Punta Arenas (53° 336 species (plus 59 probably undescribed) of shelled 37ʹ S; 70° 52ʹ W) – and in the Antarctic Peninsula: gastropod and over 87 bivalves in Antarctic waters. Punta Hanna (62° 39ʹ S; 60° 35ʹ W) and Fildes Bay (62° Specifically, in the area of the Antarctic Peninsula, 12ʹ S; 58° 54ʹ W) (Fig. 1). The samples were obtained including the South Shetland Islands, the same authors by scuba diving between 1 and 10 m depth in quadrats recorded 130 species of molluscs, i.e., low species rich- of 50 × 50 cm, which were selected randomly within ness compared to that recorded in the MBP. In more each bed. In each quadrat, all molluscs were collected, detail, the sublittoral bottoms corresponding to the and also the substrate, where Gigartina settled, was continental shelf were represented by 85 species of investigated. The rocks were subsequently scraped to gastropod and 48 bivalves (Linse et al. 2006). In addi- ensure that all the species and specimens were col- tion, molluscs exhibited several levels of species richness lected. Each macroalgal sample was placed in a plastic between different areas of the Southern Ocean and bag. In the laboratory, each sample was gently stirred adjacent areas, such as the MBP (Linse et al. 2006). to detach the associated fauna. Once detached, the However, although in recent years efforts have algae were removed from the bag and their fresh increased to better understand MBP and Antarctic mol- weight measured. Fifteen quadrats were sampled dur- luscan biodiversity (Linse 1999; Griffiths et al. 2003; ing one dive at each site, resulting in 60 quadrats per Zelaya 2005; Linse et al. 2006; Clarke et al. 2007;Aldea site (4 sites × 15 quadrats). et al. 2011;Pastorino2016), few investigations have Molluscs density was standardized to individuals focused on the ecological interaction between macro- per gram of algal fresh weight. To determine the algae and Antarctic molluscs (Amsler et al. 2015). faunal composition – and their comparison – uni- The main objective of this study was to character- variate and multivariate biodiversity analyses were ize and compare molluscan assemblages associated performed using the Primer version 6.0 statistical with Gigartina skottsbergii beds in the Strait of package (Clarke & Gorley 2005). The univariate bio- Magellan and Gigartina sp. from the Antarctic diversity measures calculated for each site were aver- Peninsula. The level of taxonomic affinity between age species richness and average species abundance. the two provinces was also tested. Spearman rank correlation analysis was conducted to determine the correlation between mollusc abun- dance and macroalgal fresh biomass. Material and methods To show significant differences in abundance and The study area was localized at four sampling sites species richness, including beds from both provinces, with G. skottsbergii and Gigartina sp. beds: two in the a nonparametric Mann–Whitney test was performed, Strait of Magellan – Punta Santa Maria, located in using the Statistica 7.0 statistical package (StatSoft Tierra del Fuego (53° 21ʹ S; 70° 27ʹ W); Punta Santa 2004; http://statistica.software.informer.com/7.0/). Figure 1. Sampling sites in the Strait of Magellan (A) and South Shetland Islands (B, C). POLAR RESEARCH 3 The specific importance of each species at each sam- species belonging to six families) and Polyplacophora pling site was determined by the similarity percentage, (seven species belonging to four families). The best- Simper (Clarke 1993). Once the most representative represented families were Littorinidae (four species) species of each group was known, complementary and Phylobryidae (four species). NMDS (Kruskal & Wish 1978) was performed to analyse For Antarctic Peninsula beds, the most abundant graphically which species contributed to the similarity of species were the bivalve Lissarca miliaris (233 indivi- each of the study areas. The data were transformed to duals) and the gastropod Laevilacunaria antarctica presence and absence, to reduce the contribution of (94 individuals), while